Studies on drug effected DNA strand breakage in cultured L1210 cells show that the hydroxyl apatite chromatography method can be utilized for quantitation of this action. The anthracycline antibiotics, actinomycin D, and bleomycin showed extensive DNA strand breakage as did hyperthermia. Hyperthermia gives additive effect to anthracycline therapy against L1210 cells in culture. Our studies on the mechanism of action of adriamycin and daunorubicin against T4 DNA polymerase show both uncompetitive and inhibition at low and high drug to DNA ratios. This can be related to intercalative and ionic binding of adriamycin to DNA. BIBLIOGRAPHIC REFERENCES: Bachur, N.R., Steele, M., Meriwether, W.D., and Hildebrand, R.C.: Cellular pharmacodynamics of several anthracycline antibiotics. J. Med. Chem. 19: 651-654, 1976. Goodman, M.F., Lee, G.M., and Bachur, N.R.: Adriamycin interactions with T4 DNA polymerase: Two modes of template mediated inhibition. J. Biol. Chem. 252: 2670-2674, 1977.